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Department
of Podiatry
Metatarsal
Length Variations
normal metatarsal formula is 2>1>3>4>5 or 2>1=3>4>5
second metatarsal is normally the longest and accepts the largest
relative load
variations in metatarsal length will cause:
· changes in relative plantar pressure distribution
· abnormal propulsion mechanics
Long
2nd metatarsal
most common variation
results in large increase in pressure under the second MPJ during
propulsion - HK formation
may also cause digital deformity secondary to footwear compression
treatment involves pressure reduction and footwear modification /
advice
Short
first metatarsal
originally described by Morton (1935)
requires first ray plantarflexion to assist in propulsion (ice-cream
sticks analogy)
may result in:
· greater pressure on 2nd MPJ
· DJD 1st and 2nd MPJs
· unstable medial column and subsequent STJ pronation
Tx with Morton's extension
Long
first metatarsal
increases pressure under 1st MPJ and limits normal plantarflexion
may result in hallux limitus / rigidus, dorsal 1st tarso-metatarsal
exostosis, HAV
treatment:
· first ray cutout / 'kinetic wedge'
· rockerbottom shoe
· surgical shortening
Morton's
foot structure
consists of:
· short 1st metatarsal
· thickened 2nd metatarsal
· hypermobile 1st ray
· posteriorly displaced sesamoids
Morton's extension:
· enables 1st met. to take part in propulsion
· decreases pressure under 2nd MPJ and strain on T-M joint
· decreases STJ pronation
Clinical
Assessment
Non-WB or WB evaluation
MPJ dorsiflexed and plantar prominence of metatarsal head palpated
and marked
recent study found no significant difference between radiographic
and clinical assessment of met. formula, ie: valid technique
(Spooner et al, 1994)
NB: The
picture from the top of the page is taken from Michaud (reference
below), page 110.
References:
Michaud
TC (1993) Foot orthoses and other forms of conservative foot care.
Williams and Wilkins, Baltimore.
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